Method and arrangement for temperature calibration

ABSTRACT

The invention concerns an arrangement on a semiconductor chip for calibrating temperature setting curve having a signal generation unit ( 2 ) for providing a first signal (I ptat1 , V ptat1 , f ptat1 ), which is proportional to the actual uncalibrated temperature T 1  of the chip. To avoid bringing the chip on a second temperature it is proposed to read a first signal (I ptat1 , V ptat1 , f ptat1 ), which is proportional to the actual uncalibrated temperature T 1  of the chip and generate a signal offset (I virt , V virt , f virt ), which is combined with the first signal (I ptat1 , V ptat1 , f ptat1 ) defining a second signal (I ptat2 , V ptat2 , f ptat2 ) and to extract a first actual temperature T 1  from the first signal (I ptat1 , V ptat1 , f ptat1 ) and a second uncalibrated temperature T 2  from the second signal (I ptat2 , V ptat2 , f ptat2 ).

The invention concerns a method for calibrating a temperature setting curve on a semiconductor chip, further it relates to an arrangement for calibrating the temperature setting curve.

For adjusting appropriate parameters of a chip a reliable temperature value is needed. This temperature value is extracted from a characteristic signal and a temperature setting curve for the semiconductor chip.

Having the exact temperature of the chip is very important, because a lot of parameters for operating the chip are related to the actual temperature, so the parameters are adapted to the actual temperature value if the temperature is vacillating. For example, for driving a display arrangement certain voltages are necessary. The supplied voltage values are dependent on the chip temperature, which is different under certain circumstances and environmental conditions. So the actual temperature of the chip is measured for adapting the required voltages.

One possibility to calibrate the temperature curve of the sensor is to calibrate only the offset or the slope of the curve. The disadvantage of this approach is that the temperature readout is only accurate at one temperature point (the calibration point). If the slope of the temperature setting curve is not accurate, the measured temperature will have a mismatch with the actual temperature. To get an accurate result of the measurement, the slope must be calibrated as well.

It is known to calibrate a temperature setting curve of a chip by using two temperature points. To get these temperature points, the chip or device has to be brought to two different temperatures. Bringing the chip on two different temperatures requires a lot time, which is longer than the overall testing time.

So it is an object of the invention to provide a method and an arrangement for calibrating the temperature setting curve on a semiconductor chip in a very short time, by maintaining the required accuracy.

The object is solved by the features of the independent claims.

The solution is based on the thought, that the temperature extracting unit could be misleaded. To achieve this misleading a signal generation unit is provided, which is able to generate a first signal and a signal offset. A first temperature point is obtained, by reading the first signal, which is proportional to the temperature. To get a second temperature point the signal generation unit generates a signal offset which is combined with the first signal, so the extraction unit reads a second signal, which corresponds to a second temperature, whereby this second temperature does not exist on the chip, since it is only virtually.

Thus the temperature extracting unit can calculate two temperature points, the first temperature point based on the first signal, which is proportional to the first actual temperature and the second temperature point based on the second signal which is a combination of the first signal and the signal offset. This second signal is proportional to a second temperature point or a so called virtual temperature point. By knowing these two temperature points it is possible to calculate the slope and the course of the real temperature curve of the particular chip. Out of this knowledge calibration values can be calculated to get a very accurate temperature curve.

This type of temperature calibration can be used in any on-chip temperature sensors.

One aspect of the present invention regards a signal generation unit which generates a current signal I_(ptat1). This first current signal I_(ptat1) is supplied to the temperature extraction unit, wherein the first temperature point T₁ is calculated. The operation of the signal generation unit is then switched to the second current signal I_(ptat2), so a current offset I_(virt) is generated and combined with the first current signal I_(ptat1). This resulting second current signal I_(ptat2) is supplied to the temperature extraction unit, which calculates the second temperature point T₂ and further calibrates the temperature setting curve. A current based architecture is easy to realize, thereby providing high accuracy, whereas only a small chip area is required.

A further aspect of the present invention regards an embodiment, wherein the first signal is realized as a voltage V_(ptat), to be supplied to the temperature extraction unit. For calibrating the chip a voltage offset V_(virt) is generated by the signal generation unit and combined with the first voltage V_(ptat1). This resulting second voltage V_(ptat2) is supplied to the temperature extraction unit, wherein the second or virtual temperature point T₂ is calculated, facilitating the calibration of the temperature setting curve. Depending of the signal extraction unit and the reference signal it can be an advantage to use a voltage based architecture. But it is easier to combine currents than voltages keeping the best possible accuracy.

A further aspect of the present invention regards an embodiment, wherein the first signal is realized as a frequency f_(ptat), which is proportional to the temperature. The calculation of the second temperature point T₂ is performed similar to the first and second above mentioned embodiments. The using of a frequency can be advantageous, if the available reference signal is a frequency, however using a frequency is more difficult than combining voltage or current signals.

The object of the invention is also solved by a method for calibrating a temperature setting curve of a temperature sensor arrangement on a semiconductor chip, the method comprising:

-   -   reading a first signal (I_(ptat1), V_(ptat1), f_(ptat1)), which         is proportional to the actual temperature T₁ of the chip     -   generating a signal offset (I_(virt), V_(virt), f_(virt)), which         is combined with the first signal (I_(ptat1), V_(ptat1),         f_(ptat1)) defining a second signal (I_(ptat2), V_(ptat2),         f_(ptat2))     -   extracting a first actual temperature T₁ from the first signal         (I_(ptat1), V_(ptat1), f_(ptat1)) and a second temperature T₂         from the second signal (I_(ptat2), V_(ptat2), f_(ptat2))

In a further embodiment of the resulting temperatures (T₁, T₂) are used for providing calibration parameters to the chip.

Further it is possible to calculate the calibration parameters on-chip or off-chip depending on the application.

Further it is possible that additional signal offsets (I_(virt2), V_(virt2), f_(virt2)) are provided for calculating more than two temperature points T_(n), so a non linear temperature setting curve can be calibrated.

In a further embodiment the signal offset (I_(virt), V_(virt), f_(virt)) is subtracted from first signal (I_(ptat1), V_(ptat1), f_(ptat1)) or added to the first signal (I_(ptat1), V_(ptat1), f_(ptat1)) defining the second signal (I_(ptat2), V_(ptat2), f_(ptat2)) which is provided to the temperature extraction unit (3).

In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, references being made to the accompanying drawings, in which:

FIG. 1 shows a block diagram of an on chip temperature sensor;

FIG. 2 shows a first embodiment of a signal generation unit according to the present invention;

FIG. 3 shows an alternative embodiment of a signal generation unit according to the present invention;

FIG. 4 shows an alternative embodiment for signal generation unit in accordance with the present invention.

FIG. 1 shows a block diagram of an on chip temperature sensor according to the present invention. The signal generation unit 2 generates a first signal, which is proportional to the temperature. This first signal is supplied to the temperature extraction unit 3 for calculating a first temperature point. Further the signal generation unit 2 generates during the calibration procedure a signal offset, which is combined to the first signal defining the second signal. By supplying the second signal to the temperature extraction unit 3 the temperature extraction unit 3 will be misleaded. The temperature extraction unit 3 calculates a second temperature point without heating the chip on a second temperature.

The signals supplied to the temperature extraction unit 3 are converted, e.g. in AD-converter 4 and the temperature extraction unit 3 calculates the actual temperature out of the supplied signal in a digital manner, by using schemes, which are implemented. These schemes are programmed and based on formulas, which will be explained in more detail below.

By this way the calibration of the temperature setting curve is performed in a very short time, e.g. during testing procedure only by having a single temperature point. The effort in particularly the chip area for generating the signal offset in the signal generation unit 2 is very low.

FIG. 2 shows a first embodiment according to the present invention. Here the first signal is realized as a current signal I_(ptat1) if the switch 21 is open. During the calibration procedure a first current I_(ptat1) is supplied to the temperature extraction unit 3, calculating a first temperature point T₁.This temperature value T₁ corresponds to the real and uncalibrated chip temperature. After calculating this temperature value T₁ the switch 21 is closed and the second current I_(ptat2) is generated. After the switch 21 is closed a voltage ΔVbe₂ appears between the two bipolar transistors BT1 und BT2. This voltage ΔVbe₂ will be converted in a current I_(ptat2) that is corresponding to the virtual and uncalibrated temperature T₂.

In the following the functionality of the bandgap circuitry will be shortly described. The OPAMP sets the voltages of the PMOS transistors P1-P4 gates in such a way that the difference between the two OPAMP-inputs is regulated to zero.

In the following the formulas for calculating the respective temperature points are discussed. At temperature T _(test) : Δvbe _(Ttest) =Vbe1−Vbe2=(kT/q)1n(n ₁ * n ₂)|T=T _(test)  (1)

Formula (1) is for calculating the first temperature point, whereas,

-   -   Δvbe_(test)=Voltage between BT1 und BT2 during first temperature         T_(test)     -   Vbe1=Basis emitter voltage BT1     -   Vbe2=Basis emitter voltage BT2     -   k=Bolzmann constant     -   T=absolute Temperature (K)     -   q=charge of an electron     -   n₁, n₂, n₃=multiplication factors, how many unity transistors         are connected in parallel     -   x=variable depending on parameters like accuracy, size of         circuitry etc.

The multiplication factors n₁, n₂, n₃ are selected in dependency on the required accuracy and the available chip area and the current consumption. The advantage of having a high value for the multiplication factor n₂ is a high Δvbe leading to a good precision. However a high n₂ requires a lot of chip area for realizing of the bipolar transistor BT2. The advantage of having a high value for the multiplication factor n₁ is a high Δvbe leading also to a good precision. The high current consumption is disadvantageous in that case, further it requires a slightly more chip area. But selecting n₁ too big will result in lower precision due to the mismatch of the current mirror. Taking a high value for the multiplication factor n₃ will lead to a higher precision, because the two temperature points are more separated, so the signal offset is higher. The drawback is an increased chip area and a higher current consumption during the calibration. A good compromise for accuracy, chip area and current consumption will be achieved with n₁=10, n₂=24, n₃=17.

The formula (2) is used for calculating the second temperature point T₂ (switch 21 closed).

For T at temperature T_(test): Δvbe ₂ =Vbe1−Vbe2=(k*T/q)* 1n((n ₁ +n ₃) * n ₂)|T=T _(test)  (2)

Using formula (1) and formula (2) the virtual temperature T₂ can be calculated with formula (3) T ₂ =T _(test)*1n((n1+n3) * n2)/1n(n1*n2)  (3)

The current signal, which is proportional to the temperature is measured and based on the physical rule I _(ptat) =Δvbe/R  (4)

FIG. 3 shows an alternative embodiment according the present invention.

In this embodiment a first voltage V_(ptat1) is generated and supplied to the temperature extraction unit 3. For generating a second voltage or a virtual voltage the switch 21 is closed and the V_(ptat2) is supplied to the temperature extraction unit 3 which corresponds to T₂.

By using this architecture a virtual temperature point can be generated. With this virtual temperature point T₂ and the T_(test) point it is possible to calculate the slope of the uncalibrated temperature curve, thereby making the calibration possible during chip testing at one single temperature, which saves time.

A further embodiment for signal a generation unit 2 for generating a virtual temperature is shown in FIG. 4. In this embodiment the current I_(ptat2) is subtracted by closing the switch 21. Thereby the second temperature T₂ will be below T₁. There are no changes required in the temperature extraction unit 3. Following formulas corresponds to FIG. 4: For T ₂ at temperature T _(test) : Δvbe ₂ =Vbe1−Vbe2=(k*T/q)*1n((n ₁ −n ₃)*n ₂)|T=T _(test)  (4)

Using Formula (1) and formula (4) the virtual temperature T₂ can be calculated with formula (5) T ₂ =T _(test)* 1n((n ₁ −n ₃)*n ₂)/ln(n ₁ *n ₂)

This embodiment is advantageous because T₂ is smaller than T_(Test). Since the temperature T_(Test) during the test procedure is typically 85 degrees, a smaller T₂ than T_(Test) will make the behaviour of the system closer to normal operation mode. However the current copy through the current mirrors introduces additional error leading to a less precise calibration. 

1. Arrangement on a semiconductor chip for calibrating a temperature setting curve having a signal generation unit for providing a first signal, which is proportional to the actual temperature of the chip, whereby a signal offset is creatable by the signal generation unit, which is combined with the first signal defining a second signal; a signal extraction unit receiving the first signal and the second signal for calculating a first temperature point based on the first signal and a second temperature point based on the second signal.
 2. Arrangement as claimed in claim 1, whereby the first signal, which is proportional to the actual temperature of the chip, is a current, a voltage or a frequency.
 3. Arrangement as claimed in claim 1, whereby the first signal and the second signal are convertible into digital signals, whereby the temperature extraction unit calculates the first and second temperature points for calibrating the temperature setting curve.
 4. Method for calibrating a temperature setting curve of a temperature sensor arrangement on a semiconductor chip, the method comprising: reading a first signal, which is proportional to the actual temperature dof the chip generating a signal offset, which is combined with the first signal defining a second signal extracting a first actual temperature T₁ from the first signal and a second temperature from the second signal
 5. Method as claimed in claim 4, whereby the resulting temperatures are used for providing calibration parameters to the chip.
 6. Method as claimed in claim 5, whereby calculating calibration parameters can be performed on-chip or off-chip.
 7. Method as claimed in claim 4, whereby additional signal offsets are provided for calculating more than two temperature points and calibrating a non linear temperature setting curve.
 8. Method as claimed in claim 4, whereby the signal offset is subtracted from first signal or added to the first signal defining the second signal, which is provided to the temperature extraction unit. 